March 21: ORD

Today is March 21st. It's the 81st day of the year. 285 days remain. It's week 12 of the year.

Unless noted, the following data is based upon observations collected by the National Weather Service, Chicago, at O'Hare International Airport (ORD) between November 1978 and last year. ORD has been the official site of record for Chicago since Thursday, January 17, 1980. Before this, the official site of record was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. Before that, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 49 and the normal low is 31. I've calculated the 33-year averages at 46 and 30.

On the warm side, in 1991 (until 2012, O'Hare's warmest March 21st) the high was 71 with a low of 49 (until 2012, that low of 49 was O'Hare's warmest of the date). Six years later, in 1997, the high was 71 with a low of 36, a 35 degree spread. Those highs of 71 were, until 2012, O'Hare's co-warmest of the date. A decade later, in 2007, the high was 67 with a low of 37, a 30 degree spread. The other warm highs were 63 in 1990 and 61 three years ago, in 2009. The record high (prior to 2012) was 77, set back in 1938. The record warmest low (prior to 2012) of 54 occurred back in 1918. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 22 of the past 33 highs (67%) were in the: 30s (12) and 40s (10). On the warm side, 11 highs (33%) were in the: 50s (4), 60s (5) and 70s (2). The 50s highs occurred in two sets of the back-to-back years of 1994/1995 and 2000/2001. O'Hare's second warmest March 21st (until 2012) was in 1975 when the high was 70 and low was 41. O'Hare registered just three highs in the 70s on the date and no 80s until this year (2012). The other pre-1979 warm highs were 67 in 1966 and 62 in 1972.

In looking back through the years to the first March at O'Hare in 1959, the following instances were notable: In 1977 the high was 38 with a low of 33, a five degree spread. In 1975 the high was a warm 70 with a low of 41, a warm day. In 1974 the high was a cold 37 degrees. In 1972 the high was a warm 62 with a low of 42, a warm day. In 1970 the high was 59 with a low of 29, a 30 degree spread. In 1968 the high was a cold 37 degrees. In 1967 the high was 38 with a low of 31, a seven degree spread. In 1966 the high was 67 with a low of 42, a warm day. In 1965 the high was 21 with a low of 8, a cold day. In 1962 the high was 39 with a low of 32, a seven degree spread. In 1960 the high was 35 with a low of 10, a cold day. In 1959 the high was a cold 37 with a low of 20, a cold day.

More recently, we had small spreads of four degrees in 1984 (35/31), five degrees in 1982 (40/35), five degrees in 2008 (34/29) and seven degrees in 2006 (33/26). There were additional large spreads of 31 degrees in 1990 (63/32) and 32 degrees in 1987 (60/28).

On the cold side, in 1986 the high was 37 with a low of 13. Three years before, in 1983, the high was 30 with a low of 21. In 2004 the high was 33 with a low of 22. Two years before, in 2002, the high was 39 with a low of 17. In 1989 the high was 35 with a low of 21. The other cold highs were 33 in 2006, 34 in 2008, 35 (1984 & 1988), 36 in 1992 and 37 in 1996. The record low of 9 was originally set way back in 1885 and tied in 1888. The record coldest high of 19 occurred way back in 1885. So March 21, 1885 was a very cold day. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 28 of the last 33 lows (85%) were in the: 20s (15) and 30s (13). Two lows were in the cold 10s (a.k.a. teens). O'Hare's coldest March 21st was in 1965 when the high was 21 (O'Hare's only 20s high of the date) and low was 8 (O'Hare's only single digit low of the date). O'Hare also had a cold low of 10 in 1960. Three lows were in the warm 40s.

Today is a major day in Chicago's snow history. At O'Hare in 1965, this was the second of seven days in which a total of 10.2 inches fell. Today just three tenths of an inch fell. In 1932 in Rockford, 11 inches fell. At the University of Chicago in 1932, a total of 8.9 inches fell from March 20-22. 7.8 inches of the total fell today, on the 21st. At O'Hare in 1983, this was the third day of a three day, 7.2 inch snowstorm. Today 3 inches fell. 2008 was the first day of a two-day storm. At O'Hare, 4.8 inches fell. Rockford had 4.7 inches and Midway had 2.6 inches. Some of Midway's precipitation was a wintry mix (freezing rain, sleet).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:26 and sunrise is at 6:54. Sunset is at 19:07 and twilight ends at 19:35. There's a total of 12 hours, 13 minutes of daylight today and 13 hours, 9 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:24 and sunrise is at 6:52. The moon is waning crescent and will be new tomorrow morning at 9:37. Illumination was 2% at midnight, will be 1% at noon and 0% at midnight tonight. Moonrise is at 6:06 this morning. Moonset is at 18:35 tonight. Moonrise is at 6:31 tomorrow morning. Moonlight time is 12 hours, 29 minutes which is 36 minutes longer than yesterday. The Spring Equinox was at 0:14 yesterday morning.

Spring began on March 12th and runs for 84 days through June 3rd. Cool Spring began on March 12th and runs for 32 days through April 12th. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 60s and 70s usually occur infrequently. April Fools' Day and Palm Sunday are in 11 days.